Opposition to reliance on non-renewable sources of energy to power our transportation sector has been yearly growing stronger along with opposition to dependence on foreign supplies of energy. The United States has long relied on petroleum products to power its transportation. However, in the last 60 years, the U.S. has gone from being energy independent to relying 70% on foreign sources of energy. Alternatives are being sought that reduce our dependence on foreign petroleum based products out of environmental and security concerns. Vehicles fully or partially powered by electricity offer a solution to these concerns.
A major hurdle in designing large electrically-powered road vehicles involves the traction motor. 3-phase alternating current induction motors are sturdy and reliable. They are capable of efficient transformation of electric power to mechanical motion. However, conventional alternating current (AC) motors require high voltage and current levels to achieve the output torque necessary to move a large vehicle in a satisfactory manner. Fulfilling these requirements can increase the risk to safety, and place higher demands on the motor drive controller's protective circuits. High operating temperatures impede the flow of current in the stator and rotor, leading to inefficient motor operation. Additionally, the overall lifetime of a motor's iron and insulation is increased by 50% for every 10 degrees Fahrenheit the motor's operating temperature is reduced.
Integrating multiple smaller AC induction motors on a common shaft has not been an effective solution to the problems presented by large AC induction motors due to the precision of manufacturing and complexity of control necessary to avoid dissimilar behavior of integrated motors resulting in reverse torque pulses and excessive vibration.
An additional problem in electrically-powered road vehicles is that in removing the combustion engine one removes the primary driver of systems critical to the safe operation of a large vehicle, especially the power steering pump and the air brakes. The combustion engine also provided for long range travel using an energy-dense fuel. Current battery technology cannot rival the energy densities seen in fossil fuels, and so no electric vehicle has yet had a driving range comparable to a similarly sized gasoline vehicle.
Electric motors have served as a primary means for propulsion in some wheeled vehicles for over a century by now, with many designs incorporating multiple sources of electrical energy, along with multiple sources of propulsion. The hybrid vehicle concept is not new. What has changed over the past century are the motor units providing the propulsion, the controls driving the motor units, the capabilities of various new energy storage technologies, and the devices assisting in the operation of modern vehicles.
U.S. Pat. No. 6,909,215 issued to Bryant describes a motor on whose shaft is mounted a number of motor modules operating on reluctance, each of which consists of two disc-shaped rotors sandwiching a disc shaped coil, increasing complexity of construction of the motors and control systems for increased flexibility without providing the safety and redundancy benefits at high power levels provided by the present invention.
U.S. Pat. No. 7,397,156 issued to Mukai et al describes a tandem rotary electric machine having a primary and secondary rotor. Mukai further describes that the secondary rotor operates at a much higher voltage than the primary rotor and operates only intermittently. The device described by Mukai does not address the problem of coupling electric motors to produce high power levels with safety and redundancy.
U.S. Pat. No. 6,034,456 issued to Osama et al describes a bearing less machine drive having two rotors that are electrically and mechanically coupled to each other through a common end ring. The device disclosed by Osama does not address the problem of coupling electric motors to produce high power levels efficiently that is addressed by the present invention. The device disclosed by Osama instead couples two rotors both mechanically and electrically to achieve stable levitation. This does not provide the benefits of high power output and increased efficiency.
A 1918 patent issued to Beach, U.S. Pat. No. 1,275,201 provides an example of the hybrid vehicle's history. The vehicle described by Beach is propelled by an electric motor powered by both a battery and an engine generator unit. Thus Beach describes a single driving source with hybrid power sources. Beach uses a direct current motor and does not provide a safe and redundant high power electric motor.
A 1974 patent issued to Waldorf, U.S. Pat. No. 3,792,327, describes a hybrid electric vehicle drive. The device described in Waldorf s patent differs from previous designs in his elaboration of the engine generator unit's operation. However the Waldorf design is limited to the control system for a generator in a hybrid vehicle and does not provide a safe and redundant high power electric motor.
A 1975 patent issued to Eastham, U.S. Pat. No. 3,866,703, includes improvements to the vehicle's transmission and control pedals. Though Eastham includes an AC induction motor and regenerative braking, he relies on conventional induction motors. As a result, Eastham's design suffers from the same problems as previous designs.